1. Field of the Invention
The invention relates to a method of reducing the volume of a mixture of filter fibers and a powder-form ion-exchange resin.
In nuclear power stations, powder-form ion-exchange resins are used in the form of precoat layers for purifying condensates and wastewater streams, for example. In order to improve the precoat behavior and the service life of the precoat layer acting as a filter, inert material in the form of short, thin filter fibers is added to the powder-form ion-exchange resin, which is also referred to below as resin powder. Those filter fibers generally are formed of polyacrylonitrile. When the precoat is being deposited on the filter, the fibers accumulate as a disordered heap. The resin powder particles are fixed in intersticial spaces of the heap. A precoat layer which is made up in this manner has a low resistance to flow and is distinguished by the fact that no cracks form. Such cracks, which are frequently caused by shrinkage processes, may frequently be observed in pure resin powder precoat layers without filter fibers.
However, the advantages that those combined precoat materials offer for the operation of power stations of that type are opposed by certain disadvantages in the disposal of the used filter materials. In other words, the used filter materials are customarily flushed, as a suspension, into high-integrity containers and are dewatered therein through built-in filter candles or multiple tube filters. The containers that are charged with the dewatered filter materials are taken to ultimate disposal in that state. Due to the filter material structure that was already described at the outset, the amount of filter material which can be introduced per unit volume is very low. In that case, the apparent compacted density of typical resin powder precoat materials is between 0.37 g/cm.sup.3 and 0.42 g/cm.sup.3 in the as-delivered state. Although drying the material decreases the volume by about 35%, if water penetrates into the containers charged with the dried filter material in the final repository, there is the danger of destruction of the package due to resulting swelling pressure.